Cysteine proteases represent a class of peptidases characterized by the presence of a cysteine residue in the catalytic site of the enzyme. Cysteine proteases are associated with the normal degradation and processing of proteins. The aberrant activity of cysteine proteases, for example, as a result of increased expression or enhanced activation, however, may have pathological consequences. In this regard, certain cysteine proteases are associated with a number of disease states, including arthritis, atherosclerosis, emphysema, osteoporosis, muscular dystrophy, inflammation, tumor invasion, glomerulonephritis, periodontal disease, metachromatic leukodystrophy and others.
An increase in cathepsin activity such as, for example, cathepsin S, contributes to the pathology and/or symptomatology of a number of diseases such as, for example, autoimmune disorders, including, but not limited to, juvenile onset diabetes, multiple sclerosis, pemphigus vulgaris, Graves' disease, myasthenia gravis, systemic lupus erythemotasus, irritable bowel disease, rheumatoid arthritis and Hashimoto's thyroiditis, allergic disorders including but not limited to, asthma, and allogeneic immune responses, including, but not limited to, organ transplants or tissue grafts. Cathepsin S is also implicated in disorders involving excessive elastolysis, such as chronic obstructive pulmonary disease (e.g., emphysema), bronchiolitis, excessive airway elastolysis in asthma and bronchitis, pneumonities and cardiovascular disease such as plaque rupture and atheroma. Cathepsin S is implicated in fibril formation and, therefore, inhibitors of cathepsin S may be of use in treatment of systemic amyloidosis.
The activity of, for example, cathepsin B in synovial fluid is significantly elevated in osteoarthritis models (F. Mehraban Ann. Rheum. Dis. 1997; 56, 108-115). Similarly, cathepsin K is a critical protease in synovial fibroblast-mediated collagen degradation (W.-S. Hou (et al.) Am. J. Pathol. 2001, 159, 2167-2177). Thus, inhibition of Cathepsin B and K, for example, is a useful method for the treatment of degenerative joint diseases such as, for example, osteoarthritis. Cathepsin K inhibition, for example, leads to inhibition of bone resorption (G. B. Stroup (et al.) J. Bone Mineral Res. 2001, 16, 1739-1746). Cathepsin K inhibitors are, therefore, useful for the treatment of osteoporosis.
It is known in the art that cathepsins play an important role in the degradation of connective tissues, the generation of bioactive proteins and antigen processing. They have been implicated in osteoporosis, muscular dystrophy, bronchitis, emphysema, viral infection, cancer metastasis and neurodegenerative diseases, such as Alzheimer's disease and Huntington's disease. Recently, increased interest in cathepsin inhibitors has been generated with potential therapeutic targets, such as cathepsin K or cathepsin L for osteoporosis and cathepsin S for immune modulation (W. Kim., K. Kang. Expert Opin. Ther. Pat. 2002, 12, 419-432). An increase in cathepsin K or B activity contributes to the pathology and/or symptomatology of a number of diseases. Accordingly, molecules that inhibit the activity of cathepsin protease are useful as therapeutic agents in the treatment of such diseases.